(1) Field of the Invention
The present invention relates to an optical pickup that is used to read and write information from and onto an optical recording medium, and to a method for manufacturing this optical pickup.
(2) Description of the Related Art
In recent years, optical recording media, such as a compact disc (CD) and a digital versatile-disc (DVD), are increasingly used to store various types of information, and such recording media are rapidly becoming in widespread use. An optical pickup is usually used as an optic device that performs a read from and a write onto such an optical recoding medium.
FIG. 1 shows a construction of a conventional optical pickup 400 in a vertical section view.
As shown in the figure, the optical pickup 400 has a movable member 406 which is movable and which carries an objective lens 401 and coils 405. A fixed member 407 supports the movable member 406 almost horizontally via four wires 412 which are positioned in parallel to one another. The fixed member 407 is fixed to an optical base 409.
Since this figure is a section view obtained by vertically cutting the optical pickup 400, two out of the four wires 421 are not shown in the figure.
In addition to the fixed member 407, a yoke 410 that supports a magnet 411, an integrated component 402, a collimating lens 420, and a mirror 403 are positioned onto the optical base 409.
The integrated component 402 contains a semiconductor laser and a photodetector. The semiconductor laser emits a laser beam, which is then collimated by the collimating lens 420 to generate a collimated beam. The mirror 403 has an optical path of the collimated beam changed ninety degrees upward to have the beam enter into the objective lens 401, which then focuses the beam onto the recording surface of an optical recording medium 412. The beam is then reflected on the surface of the recording medium 412, and reverses along the above optical path. The photodetector in the integrated component 402 detects this beam, so that a signal recorded on the recording medium 412 can be read by the optical pickup 400. Hereafter, the beam reflected on the recording medium 412 is called xe2x80x9ca return beamxe2x80x9d.
Optical recording media tend to vertically vibrate when rotated. Accordingly, it is necessary to keep positioning the recording surface of the optical recording medium 412 within the depth of field of the laser beam L1 converged by the objective lens 401 by moving the objective lens 401 in a direction of its optical axis.
Eccentricities in the rotation of the optical recording medium 412 make it also necessary to reposition the laser beam L1 so that it correctly follows a track on the optical recording medium 412. Accordingly, an optical pickup is required to have an adjusting function and an error detecting function for having the laser beam correctly focused on a recording medium, and for having the laser beam correctly follow a track.
The conventional optical pickup 400 therefore has the photodetector in the integrated component 402 detect a focusing error and a tracking error by receiving the return light, and suitably controls currents supplied to the coils 405. Currents passed through the coils 405 interact with a magnetic filed generated by the magnet 411 fixed to the yoke 410 so that Lorentz forces are generated. As a result, the objective lens 401 moves in a focusing direction (i.e., a direction of the laser beam L1 being projected), and in a tracking direction (i.e., a direction which traverses tacks) that has the laser beam L1 correctly projected onto a track of the recording medium 412. By performing these operations, the optical pickup 400 can accurately perform a write onto and a read from the optical recording medium 412.
With this conventional optical pickup 400 that moves the objective lens 410 in this way, the integrated component 402, the collimating lens 120, and the mirror 403 are all fixed to the optical base 409 although only the objective lens 401 is movable to correct the focusing error and the tracking error. As a result, a displacement is generated between the optical axis of the objective lens 401 and a principal ray of the laser beam emitted by the semiconductor laser, so that a lens aberration is generated. This decreases optical properties of the optical pickup 400, and so precision of the optical pickup 400 for a write onto and a read from the optical recording medium 412 decreases.
One method to solve the above problem is to position the semiconductor laser, the photodetector, and the collimating lens 420 into the movable member 406 that supports the objective lens 401 so as to maintain the constant positional relationship between these optical components all the time and thereby prevent optical displacements from being generated.
FIG. 2 is a simplified diagram showing a construction of an optical pickup 500 achieved according to this method.
As shown in the figure, the optical pickup 500 includes a movable enclosure 505 that carries an objective lens 501, a semiconductor laser 502, a photodetector 503, and a beam splitter 504. (Hereafter, an optical pickup that has a movable enclosure carrying all the optical components of the optical system is called an xe2x80x9coptical-component-integrated optical pickupxe2x80x9d.) The movable enclosure 505 is fixed to a fixed member 506 via four wires 507 in a manner that allows the movable enclosure 505 to move in both the focusing direction and the tracking direction. The bottom portions of the movable enclosure 505 is also combined with a flexible printed circuit 508, which supplies electric power to the semiconductor laser 502 and the photodetector 503, and transfers a signal to/from them.
When the entire optical system is included in the movable enclosure 505 in this way, displacements, due to movements of the objective lens 501, no longer occur between the optical axis of the objective lens 501 and the principal ray of the laser beam. However, the flexible printed circuit 508 exerts an unnecessary force to the movable enclosure 505 which is suspended by the four wires 507. This not only prevents smooth vertical and horizontal movements of the movable enclosure 505, but also produces unnecessary resonance due to the elasticity of the flexible printed circuit 508 when the enclosure 505 moves. This prevents the optical pickup 500 from correctly following a track, and therefore the construction of the above optical-component-integrated optical pickup becomes meaningless. Hereafter, the capability of an optical pickup correctly following a track is called a xe2x80x9ctrackabilityxe2x80x9d of the optical pickup.
The conventional optical pickup 500 also has the following problems due to its supporting construction with the four wires 507.
The four wires 507 have the same length and the same thickness, and are made of the same material. As a result, each wire 507 has the same elastic coefficient in both the focusing direction and the tracking direction, and ends of these wires 507 are burdened with an almost uniform mass (i.e., one-fourth the mass of the movable enclosure 505). This results in each wire 507 having almost the same resonance frequency in both the tracking direction and the focusing direction. Should an external perturbation occur in either of these two directions, the other direction is also affected by this perturbation. This can result in, at worst, the movable enclosure 505 moving in circles, and make it difficult to have the laser beam correctly follow a track.
In order to solve the above problems, the present invention aims, as the first object, to provide an optical pickup that contains a movable enclosure carrying the whole optical system, which performs operations from emission of a laser beam to reception of a return light, and that is capable of keeping correctly focusing the laser beam on a track of an optical recording medium.
The present invention also aims, as the second object, to provide a method for manufacturing the above optical pickup.
The first object can be achieved by an optical pickup, including: a semiconductor laser for emitting a laser beam; an objective lens for focusing the emitted laser beam on an optical recording medium; a first member for carrying at least the semiconductor laser and the objective lens; a second member; and a plurality of supporting members that are elastic and each contain a first portion and a second portion which are respectively connected to the first member and the second member, wherein the second member supports the first member via the plurality of supporting members in a manner that allows the first member to move in predetermined directions with respect to the second member, wherein the plurality of supporting members include at least two supporting members that are electrically conductive, and wherein the at least two electrically conductive supporting members include electrically conductive supporting members that function as lines to conduct power to the semiconductor laser.
For this construction, the conductive supporting members are also used as lines for driving the semiconductor laser so that a flexible printed circuit is no longer necessary for the present optical pickup of the optical-component-integrated type. This increases optical properties of an optical pickup. In addition, a number of parts constituting one optical pickup can be reduced, and so production efficiency enhances.
Here, the supporting members that function as the lines to conduct power may have a larger surface area than other electrically conductive supporting members.
For this construction, heat generated by the semiconductor laser can be released via the supporting members of a larger surface area.
Here, a number of the plurality of supporting members may be at least six, and the plurality of supporting members may be substantially parallel in a longitudinal direction of the plurality of supporting members.
When at least six supporting members are used in this way, variations in properties of different supporting members can be averaged, which allows the optical pickup to smoothly follow movements of a recording surface of an optical recording medium.
Here, the second member may contain a concave in which a base portion of at least one supporting member is present, and the concave may be filled with a damping material that has viscoelasticity so that the base portion is surrounded by the damping material.
With this construction, abnormal resonance generated by the supporting members can be suppressed.
Here, the plurality of supporting members may include a first supporting member and a second supporting member that have different mechanical resonance frequencies.
When the optical pickup contains the plurality of supporting members having different resonance frequencies, a resonance factor for a certain frequency can be reduced. As a result, degradation in precision with which the optical pickup performs a write and a read can be prevented.
For this reason, it is preferable that the first supporting member and the second supporting member are differently shaped or have different widths. It is alternatively possible that the plurality of the supporting members are divided into a plurality of groups, and the second member has a plurality of concaves, in each of which base portions of supporting members of a same group are present. The plurality of concaves may be filled with at least two types of damping materials that have different viscoelasticity.
Here, the plurality of supporting members may be composed of layers of at least two types of members, and the at least two types of members may include a metal plate and an insulating plate. At least two metal plates and at least one insulating plate may be alternatively layered to form each supporting member.
This construction provides a necessary number of conductive members for supplying power to optical components positioned in the first member while reducing the size of the optical pickup as a whole.
Here, each insulating plate may be made of a damping material that has viscoelasticity.
This construction gives a function for suppressing resonance to each supporting member.
Here, the optical pickup may further include a driving unit that has two driving coils which generate a driving force to move the objective lens in a focusing direction and a tracking direction, and the two driving coils may be positioned in the first member in an approximately central portion in a direction perpendicular to: (a) a direction of an optical axis of the objective lens; and (b) a longitudinal direction of the supporting members. Out of the plurality of supporting members, at least six supporting members may be electrically conductive, and the plurality of supporting members may be positioned symmetrically with respect to a position at which the driving coils are positioned, with a number of supporting members on each side of the position being the same. On each side of the position, at least two of the at least six electrically conductive supporting members may be positioned closer to the driving coils than other supporting members.
With this construction, the same number of elastic supporting members are positioned symmetrically with respect to a position of the driving coils. As a result, the plurality of supporting members can movably support the first member while achieving a suitable balance. In addition, when the conductive supporting members closer to the driving coils are used as lines that supply power to the driving coils, a wiring process for other components, such as the semiconductor laser, becomes easier.
Here, the first member may further contain: a first reflecting unit that has a first surface which reflects a laser beam emitted by the semiconductor laser; and a second reflecting unit that has a second surface which reflects the laser beam, which has been reflected by the first surface, toward the objective lens. The first surface and the second surface may be parallel.
For this construction, a principal ray of a laser beam, which has been emitted by the semiconductor laser and enters into the first reflecting unit, is in parallel to a principal ray of the laser beam which has been reflected by the second reflecting unit and enters into the objective lens. As a result, a certain distance can be maintained between these two principal rays even when the semiconductor laser is not precisely positioned during assembly. Accordingly, the precision in positioning optical pickups during assembly can be reduced.
The second object of the present invention can be achieved by a method for manufacturing an optical pickup, the optical pickup including: a first member that carries optical components, which include (a) a semiconductor laser component that emits a laser beam and (b) an objective lens that focuses the laser beam onto an optical recording medium; a second member; and a plurality of supporting members that connect the first member with the second member in a manner that allows the first member to move. The method includes: a supporting member positioning step for positioning at least six supporting members between the first member and the second member, the first member and the second member being positioned at a predetermined interval; and a supporting member connecting step for connecting each supporting member to the first member and to the second member so as to have a substantially uniform stress distributed to each supporting member.
With this method, a uniform stress can be distributed to each supporting member during a connection process so that abnormal resonance can be suppressed when the optical pickup is in actual use and operates.
Here, the plurality of supporting members may be electrically conductive, and the supporting member connecting step may contain a step for soldering at least one end of each supporting member to at least one of the first member and the second member. Alternatively, the supporting member connecting step may contain a step for connecting at least one end of each supporting member to at least one of the first member and the second member, using ultraviolet-hardening resins, or melted glass.
With this method, a supporting length of each supporting member can be made the same by adjusting an amount of solder, ultraviolet-hardening resins, or melted glass. As a result, stress can be further evenly distributed to each supporting member. Note that the aforementioned xe2x80x9csupporting lengthxe2x80x9d refers to a length between two connected portions of each supporting member, and the two connecting portions are connected to the first member and the second member, respectively.
The second object can be also achieved by a method of for manufacturing an optical pickup, the optical pickup including: a first member that carries optical components, which include (a) a semiconductor laser component that emits a laser beam and (b) an objective lens that focuses the laser beam onto an optical recording medium; a second member; and a plurality of supporting members that connect the first member with the second member in a manner that allows the first member to move. The method includes: a plate processing step for processing two electrically conductive plates to form two structural members that have a shape of a plurality of supporting members linked to an outer part of each conductive plate; and a first member forming step for having the two structural members held so that a predetermined positional relationship between the two structural members can be maintained, and forming at least the first member, out of the first member and the second member, in predetermined portions of the plurality of supporting members.
For this method, a process to connect each supporting member to at least the first member does not need to be independently performed, so that production efficiency can be enhanced. Also with this method, at least the first member is formed, with a position of each supporting member being fixed. This prevents the supporting members from being distorted, and so suppresses variations in properties of different optical pickups.
Here, the plate processing step may further include a step for performing a bending process on portions of supporting members in at least one of the two structural members.
When a terminal portion of each supporting member of at least one of the two structural members is bent as a sub-portion and brought to a position suitable to be connected to the optical components such as the semiconductor laser, this connection process can be facilitated.
In the first member forming step, the first member and the second member may be simultaneously molded out of resins in a manner that the predetermined portions of the plurality of supporting members are embedded in the first member and the second member.
With this method, a molding process for the first member and the second member can be performed simultaneously with a connection process for each supporting member to the first member and the second member. This highly facilitates the production efficiency.
In the above first member forming step, xe2x80x9cinsert moldingxe2x80x9d is performed to form the first member and the second member. The insert molding refers to molding methods such as injection molding and transfer molding, and each supporting member becomes integral with the optical pickup through this insert molding. For the optical pickup of the present invention, injection molding, which uses melted resins, should be preferably performed to reliably prevent the supporting members from being distorted during molding.